A motor control center is a multi-compartment steel enclosure with a common bus system to distribute electrical power to one or more individual motor controllers or starter buckets mountable within the compartments. Motor control centers are most often used in factories and industrial facilities which utilize high power electrical motors, pumps, and other loads. The individual starter buckets are commonly referred to as “buckets” and are typically constructed to be removable, pull-out units to be installed in the motor control center enclosure. For safety purpose, the motor control center may comprise a sealable door to sealably enclose the modules or buckets in the motor control center. Alternatively, the motor control center may comprise a plurality of sealable doors, each for sealably enclosing a module in the motor control center.
The modules may contain various motor control and motor protection components such as motor controllers, starters, contactor assemblies, overload relays, circuit breakers, motor circuit protectors, various disconnects, and the like, for operating high voltage motors. The modules connect to the supply power lines of the motor control center and conduct supply power to the line side of the motor control components provided therein, for operation of motors.
Typically, when installing or removing the starter buckets, the corresponding power supply lines are connected or interrupted, respectively. For example, to remove such a module, a sealable front door of the module or of the motor control center is opened and an operator manually pulls on the module to separate the line connectors, or “tabs,” from the bus system, thereby disconnecting power supply. Installation of the module is accomplished in a similar manner, wherein the operator manually pushes the module into a compartment of the motor control center to engage the bucket tabs with the bus system, and thus connect the system to supply power. The line connectors or tabs may be difficult to maneuver manually when an operator is handling the entire bucket or when the tabs are not visible.
Various techniques have been evolved to improve upon the manual installation and disconnection of modules and supply power connections from live supply power lines, risers, and/or a vertical bus of a motor control center. For example, systems have employed pivotable handles inside the modules to pivot the electrical connectors away from the supply lines. However, many of these systems require that the module's door shall first be opened to manipulate the handles and line connectors.
Thus, currently available maintenance and testing methodology in respect of the starter buckets involves removal of the starter buckets, while the motor control center still has electricity running through the vertical bus bars (an energized state). For example, an operator may need to manually push a starter bucket inwardly, while the motor control center door is open, to engage the receiver clamps. The clamps are usually female connectors immovably mounted onto the back of the starter bucket that engage with the copper bus conductors, which are usually male connectors.
Such a process is dangerous procedure since the sealable door must be open, and accordingly the operator is exposed directly to electrical conducting components. If any of the electrical conducting components malfunction, an event called an arc flash can result, which can grievously injure or even kill the operator.
Further, prior art starter buckets provide only two states (on/off). When an operator needs to conduct maintenance or tests to a starter bucket, the operator has to open the motor control center's door, and conduct the maintenance or tests while the door is open. Although the motor to be controlled is turned off, the operator is exposed to the energized electrical cables within the motor control center, thereby increasing the risk of injury from an arc flash that could occur from even a simple mistake such as dropping a tool onto an energized electrical cable contact. Due to industry work practices and the design of prevalent motor control center in industry, it is not possible to simply close the door to provide the desired protection throughout maintenance or tests.
It is therefore an object to provide a novel method of supplying power to motor control components that minimizes the risk to an operator and a motor control center employing same.